Which AFAIK Apple does not use. I have RCS enabled on my Android phone but it only works to other Android users who have a compatible phone that also has RCS. S

Which AFAIK Apple does not use. I have RCS enabled on my Android phone but it only works to other Android users who have a compatible phone that also has RCS. Still does not resolve the OP's issue that Apple refuses to send/receive messages to/from other vendors' devices unless it is via SMS/MMS. It's a sad state of affairs indeed.